Safety of occupants in vehicles is an important concern to manufacturers of the vehicles and to the occupants of the vehicles. The manufacturers have disposed seat belts, some partially. or wholly inflatable, and inflatable air bags in the vehicles to protect the occupants when collisions involving the vehicle occur. An inflatable member (this term is used herein to describe an air bag as well as an inflatable belt or an inflatable belt portion) becomes inflated upon the occurrence of a collision involving a vehicle to reduce the occupant's velocity below unacceptable rates and to limit the occupant's movement to enhance the occupant's safety. Many manufacturers have started to provide inflatable members for occupants of the front driver seat.
Perhaps the most significant consideration in a vehicle containing an inflatable member relates to the fact that such a member cannot begin to restrain the occupant's motion during the vehicle collision until the occupant has moved into engagement with such member. Particularly in the case of air bags, which are typically deployed from the dashboard or steering wheel, this wastes an important portion of the time and deceleration space available to protect the occupant against injury. This markedly reduces the occupant's protection from the level which can be provided if the restraint is initiated before the occupant has moved within the vehicle after the vehicle collision.
Non-inflatable seat belts now in use almost immediately engage the occupant when a collision involving a vehicle occurs. However, such seat belts suffer from certain significant disadvantages. For example, although certain selected designs of seat belts can, through the use of pre-tensioning devices, begin a restraint of the occupant earlier than the restraint provided by an air bag, such belts do not provide for control of the occupant's head motion. This shortened deceleration time, however, has caused markedly higher decelerations and loadings, at least of the occupant's head, and has produced less than desirable results from the standpoint of injury thereto.
Seat belts are also often of narrow physical construction and thus have not provided for the distribution of the restraining loads over wide areas of the occupant's body. This has resulted in unnecessarily high loads being imposed upon the occupant over the limited portion of the occupant's body in engagement with the seat belt when a collision involving the vehicle occurs. Additionally such belts have possessed an elongation which, in many situations, has allowed the head of an occupant to strike the steering wheel or the dash board when the occupant has been seated in a front seat.
Furthermore, the spooling out of the webbing material in the seat belt and the stretching of the seat belt have contributed to an increased duration of the unrestrained motion of the occupant. This in effect has delayed the onset of any effective restraint. This has meant that the motion of the occupant has had to be brought to a stop in a shorter time than would have been possible if the seat belt had not elongated. This has contributed to the production of undesirably high rates of motion on the occupant during the restraint imposed by the seat belt on the movement of the occupant.
Even the use of inflatable seat belts of the types known in the prior art does not overcome all of the deficiencies and disadvantages discussed above. Prior attempts at eliminating these deficiencies and disadvantages with inflatable belts have included seat belts with a pair of inflatable sections within the belt and have additionally required the inflation of these sections to be accomplished by larger than desirable inflators. Previous attempts at producing satisfactory inflatable belts have also resulted in serious problems with storing the pair of inflatable sections in the vehicle and have required these inflatable sections to occupy areas which interfere with entrance and egress of the occupant respectively into and from the vehicle.
The deficiencies and disadvantages of prior art inflatable seat belts have also required the inflators to be positioned at the releasable coupling member and the retainer to be positioned at the sides of the seats. This duality of inflatable sections has caused many significant problems. One of these has been that the inflatable gases have had to pass through conduits located at the buckle attachment point of the belts that are in themselves releasable. This makes the belts and the inflator difficult to package and to operate.
It can be seen that the inflatable belts with dual inflatable sections have had to be attached to mechanisms which allow for variable lengths of the belts to be deployed due to variable sizes and positions of the occupants within the vehicle. This has required the inflator to be located at the buckle location with the aforementioned deficiencies or has required the heavy mass of the inflator to be contained within the inflatable sections of the seat belts. Furthermore, the duality of inflatable sections has required additional inflators, squibs, wiring and the like to be used since both of the inflatable sections in the pair have had to be simultaneously inflated.
Inflatable seat belts known in the prior art have other significant deficiencies and disadvantages. For example, they do not adequately protect the occupant's neck and head in a side collision. Furthermore, they also do not adequately protect the occupant's lower extremities. This results from the fact that the front seat occupant's lower extremities tend to slide forward against the instrument panel at the time of the collision while the occupant in the rear seat tends to slide against the rear of the front seat. This has caused the occupants to incur injuries to the lower extremities.
The inflators associated with prior inflatable seat belts have included combustible materials and associated apparatus which have operated in an inefficient thermodynamic manner. This has required excessive amounts of pyrotechnic materials to be provided in the inflators so that the size and weight of the inflators have had to be increased to undesirable proportions. The amount of the pyrotechnic material required in the inflators of the prior art have been roughly between fifty percent (50%) to one hundred percent (100%) more than the pyrotechnic material used in the inflator of this invention. As a result, acceptable packaging of the inflatable belts and the inflator within a vehicle has been precluded.
The configuration and composition of the combustible materials used in existing inflators have also produced relatively slow inflation systems. These slow inflation systems, while useful for air bags, have not been useful for inflatable seat belts since such restraints have to deploy in less than one fourth of the time for the deployment of a typical air bag. This has been necessitated by the fact that the inflatable belt and the inflatable side bag have to provide occupant protection from side impacts. Furthermore, the deceleration distance of a vehicle involved in a side collision and the time interval between the initiation of the side impact against the vehicle and the striking of the occupant against an interior vehicle surface are greatly reduced relative to the distance and time for a front impact.
The combustible materials for some of these systems have also required filters to collect the solid particulates that are produced. The solid particulates required to be filtered in such prior art systems have been excessive. Other systems have been required to utilize pyrotechnic grains. These grains have been of such size that grain fracture and cracking have occurred and have caused variations in the combustion surface, thereby detrimentally affecting the burning rates within the grains and hence the inflation time.
Furthermore, when large grains have been utilized with slow burning rates, the variations in performance over the range of operating temperatures has been undesirably large. For example, assuming a 40-50 millisecond function time, the changes in the burning rate of the pyrotechnic. material have caused the function time of the inflator to vary by approximately .+-.20% when the temperature has been varied between 175.degree. F. and -65.degree. F. This has resulted from changes in the burning rate of the pyrotechnic material with variations in the operating temperature. This considerable percentage change in the burning rate has produced a change in overall function time of approximately 15-20 milliseconds, an appreciable portion of the time available to an air bag to decelerate the movement of the occupant. The change in overall function has produced a resultant variation in protection.